Switch-mode power supplies (SMPSs) may generally have the demand to provide a high total efficiency over the entire output power range and a low stand-by power consumption in a so-called “no load” operation mode, in which no load is connected to the output of the SMPS.
In a conventional SMPS, there exists the attempt to optimize the system costs by using as little components as possible. Usually, the following three main criteria may be tried to be optimized: “high total efficiency”, “low stand-by power consumption”, and “low system costs”.
In order to achieve a high total efficiency, conventionally a resonant converter is used for the main power stage, which, however, does usually not achieve the required low power consumption in the stand-by operation mode.
Furthermore, there is the attempt to achieve a “no load” stand-by power consumption below 5 mW, which is also referred to as “zero power”.
In a first conventional approach, an additional auxiliary power supply is provided in addition to the main power stage. This approach is usually provided in a complex system such as in a LCD-TV set. The main power stage is switched off in the stand-by mode. The auxiliary power supply is usually dimensioned for low power and thus for a low power requiring load. A load requiring more power is supplied by the main power stage. This results in a main power stage having a plurality of output phases. This results in high costs, since an additional DC-DC SMPS circuit is provided for a particular main power stage.
In another approach, which does not provide an auxiliary power supply in addition to the main power stage, a specific burst mode of the main power stage is provided to reduce the average power consumption to a minimum. However, the specific burst mode has the disadvantage of introducing a ripple into the output voltage.
Various implementation concepts are usually provided:
In one approach, a controller TEA 1713 from NXP Semiconductors is provided as a controller for a main power stage of a resonant LLC converter for a notebook adapter. In this approach, a comparator evaluates a feedback output signal provided from an optocoupler. A controller deactivation signal to deactivate the controller is generated in case that the level of the evaluated signal becomes lower than a load threshold. In case the level of the evaluated signal becomes higher than an upper threshold, a controller activation signal to activate the controller is generated.
This approach is altered in another approach, namely in the active-burst mode configuration in the CoolSET circuit available from Infineon Technologies AG in that comparators are integrated in the controller component, wherein the comparators are configured to evaluate the signals coming from the optocoupler.
Both previously described approaches have in common that they provide an evaluation circuit and a control circuit, which are completely acting on the primary side of the converter. One result of these approaches is that the controller component usually needs to remain active during the switch-off period. Thus, the power consumption associated therewith limits the maximum switch-off time. In case the controller component would be deactivated during the switch-off period, the response time in response to an abrupt load change might be extended, since the own power supply may have been interrupted for too long. Another effect may be caused by the fact that the output voltage may not be directly measured at the secondary side, since the arrangement including the optocoupler and the regulatory circuit at the secondary side usually only transmits an error signal to the controller component at the primary side, wherein the error signal serves as a basis for the generation of the pulse width modulation.
Another approach provides the entire evaluation and control functions at the secondary side of the SMPS. This may result in increased system costs.